Cryptocurrency Café UVa cs4501 Spring 2015 David Evans Class 23: Blooming Sidechains!

Plan Bloom Filters – Design and Analysis – Use in Bitcoin Merged Mining Sidechains 1 Thursday, 6pm Commerce School 223 “Entrepreneurial and Career Ventures in the world of Digital Currency” Panel Friday, 10:45am Rice 242 Suman Jana, “Rise of the Planet of the Apps: Security and Privacy in the Age of Bad Code” Project Presentations will be April 20, 22 and 27.

2 32 GB

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SPV Nodes 4 Simplified Payment Verification SPV Wallet Full Node filter blocks matching filter

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Bloom Filters 7

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Conventional Hash Table 9 Store collection of N b -bit elements, using k > N cells. H is pseudorandom function H(x)  [0, k)

Conventional Hash Table 10 Store collection of N b -bit elements, using k > N cells. H is pseudorandom function H(x)  [0, k)

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12 How does Bloom’s application compare to use by bitcoin SPV nodes?

Bloom Filter Design 13

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16 Probability of false match: (1 – (1 – 1/m) kn ) k m : bits in array k : number of hashes n : number of elements

17 Probability of false match: (1 – (1 – 1/m) kn ) k m : bits in array k : number of hashes n : number of elements

18 Do Bloom filters really provide privacy?

Merged Mining 19

20 Pointcoin 0 Pointcoin 1 Pointcoin 6764 … Bitcoin 0 Bitcoin 1 Bitcoin … Difficulty: 8,324,713 Hash rate: ~0 TH/s Difficulty: 49,446,390,688 Hash rate: 310K TH/s Should PointCoin Pizza be worried?

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SHA-256 Proof-of-Work Cryptocurrency 22

Merged Mining 23 Goal: Enable using same hashing power to mine both Bitcoin and Namecoin (with different difficulty)

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27 Pointcoin 0 Pointcoin 1 Pointcoin 6764 … Bitcoin 0 Bitcoin 1 Bitcoin … Difficulty: 8,324,713 Hash rate: ~0 TH/s Difficulty: 49,446,390,688 Hash rate: 310K TH/s Namecoin 0 Namecoin 1 Namecoin … Difficulty: 16,527,985,062 Hash rate: 110K TH/s

Namecoin Bug 28

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Charge Projects should be making good progress now! 30 Thursday, 6pm Commerce School 223 “Entrepreneurial and Career Ventures in the world of Digital Currency” Panel Friday, 10:45am Rice 242 Suman Jana, “Rise of the Planet of the Apps: Security and Privacy in the Age of Bad Code” Project Presentations will be April 20, 22 and 27.